1. Field of the Invention
The invention relates to glow plugs and a method for the production of glow plugs.
2. Description of the Related Art
As shown in FIGS. 1, 2(a) and 2(b), a conventional glow plug has a glow tube 5 without additional tapering and without additional compaction of the glow rod tip. The glow tube 5 has an internal heating coil 4 which is embedded therein using a ceramic filling 3. At the tip of glow tube 5 on the combustion chamber side, the heating coil 4 is connected with the glow tube 5 by welding 6. At the opposite end of the glow tube 5, the heating coil 4 is connected with a connection pole 1. The front area 5a on the combustion chamber side of glow tube 5 is reduced cylindrically according to the known feed method.
As shown in FIGS. 3(a) and 3(b), in order to improve the compaction in the area of the combustion chamber side of the glow tube, the area 5a above the tip of the glow tube 5 is reduced from diameter D1 to diameter D2. In particular, at the glow tube tip 5a, the area is reduced using a so-called feed process whereby either continuous cylinders or a linear taper towards the tip of the heating rod are obtained. With this process, the glow rod is inserted into a swaging tool having a lead-in inclined area whereby the diameter is reduced by the swaging process and the axial feed of the glow tube.
The reduction in diameter that results in using the feed process, however, leads to unsatisfactory compaction precisely in the critical area directly behind the welding of the heating coil and the glow tube tip. Equally, there is little opportunity for more complex shapes of the glow tube area on the combustion chamber side, which influence glow behavior, glow distribution and the life of the glow plugs, or expansion of new possibilities for glow plug applications.
An object of the invention is to enhance the compaction in the glow tube tip while avoiding the disadvantages of the related art. In this regard, a new shaping of the tip area of the glow tube expands new possibilities for applications, in particular, the possibility of fitting other components.
The object of the invention may be achieved using a method for producing glow plugs having an internal heating coil and optionally regulating coils that are embedded in an annular space of the glow using a ceramic filling, whereby a compaction of the area on the combustion chamber side of the glow tube is performed using a recessing-reducing process with an radial feed. The recessing-reducing process is performed using a recessing tool having a pair of tool elements or stamps with stamping faces that have several zones that are arranged at an angle relative to one another. Alternatively, the stamping faces may be curved in a convex and/or concave manner. Moreover, the area on the combustion chamber side of the glow tube has band-shaped or groove-shaped neck.
Accordingly, the method and apparatus in accordance with the invention are advantageous since they result in a compaction or deformation by way of the recessing-reducing process whereby the glow tube is positioned in the recessing tool so that the stamps act radially on the glow tube and compact the glow tube to the desired diameter. As a result, a more uniform compaction occurs since an axial feed does not take place in this compaction phase so that in the presence of a solely radial action of the tool stamps, the material and coil of the glow tube are not axially displaced.